KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 44 insertions, 0 deletions

diff --git a/arch/x86/boot/bitops.h b/arch/x86/boot/bitops.h
new file mode 100644
index 000000000..79e159715
--- /dev/null
+++ b/arch/x86/boot/bitops.h
@@ -0,0 +1,44 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* -*- linux-c -*- ------------------------------------------------------- *
+ *
+ *   Copyright (C) 1991, 1992 Linus Torvalds
+ *   Copyright 2007 rPath, Inc. - All Rights Reserved
+ *
+ * ----------------------------------------------------------------------- */
+
+/*
+ * Very simple bitops for the boot code.
+ */
+
+#ifndef BOOT_BITOPS_H
+#define BOOT_BITOPS_H
+#define _LINUX_BITOPS_H		/* Inhibit inclusion of <linux/bitops.h> */
+
+#include <linux/types.h>
+#include <asm/asm.h>
+
+static inline bool constant_test_bit(int nr, const void *addr)
+{
+	const u32 *p = addr;
+	return ((1UL << (nr & 31)) & (p[nr >> 5])) != 0;
+}
+static inline bool variable_test_bit(int nr, const void *addr)
+{
+	bool v;
+	const u32 *p = addr;
+
+	asm("btl %2,%1" : "=@ccc" (v) : "m" (*p), "Ir" (nr));
+	return v;
+}
+
+#define test_bit(nr,addr) \
+(__builtin_constant_p(nr) ? \
+ constant_test_bit((nr),(addr)) : \
+ variable_test_bit((nr),(addr)))
+
+static inline void set_bit(int nr, void *addr)
+{
+	asm("btsl %1,%0" : "+m" (*(u32 *)addr) : "Ir" (nr));
+}
+
+#endif /* BOOT_BITOPS_H */